One nanofabrication technique may include a controlled breakdown (CBD) of a thin solid-state membrane to form nanopores in the membrane at the nanoscale. The technique employs a high electric field (e.g., ˜1V/nm) that is applied across the membrane, which is immersed in an electrolyte solution. The presence of a tunneling current through the membrane induced by the high electric field leads to the formation of locally conductive defects at hotspots on the membrane, and causes a breakdown when a connected path of such defects exists across the membrane. The by-product of the breakdown reaction is easily removed by the fluid, and the formation of an individual nanopore is indicated by a sudden increase in the level of current measured through the membrane, or the appearance of an ionic current at low electric field strength (e.g., ˜0.01V/nm, values at which the rest of the membrane is insulating).
Using the CBD based technique, nanopores as small as 1-nm in diameter can be made, and can be further enlarged using moderate electric fields with sub-nm precision. The field can be applied continuously or pulsed between high and low values during fabrication. Further details regarding the CBD technique may also be found in Kwok, H.; Briggs, K; and Tabard-Cossa, V.; “Nanopore Fabrication by Controlled Dielectric Breakdown”—PLoS ONE 9(3): e92880 (2014) and in U.S. patent application Ser. No. 14/399,071 entitled “Fabrication of Nanopores using High Electric Fields” which is incorporated in its entirety herein by reference. Details regarding enlarging the nanopores can be found in Beamish, E.; Kwok, H.; Tabard-Cossa, V.; and Godin, M.; “Precise control of the size and noise of solid-state nanopores using high electric fields”—Nanotechnology 23, 405301, 7 pages (2012), and in U.S. patent application Ser. No. 14/399,091 entitled “Method for controlling the size of solid-state nanopores” which is incorporated herein by reference.
The fabrication process using the CBD technique can be stochastic, both in terms of the time-to-breakdown and the location of the nanopore on the membrane. For instance, only one nanopore is formed as long as the electric field is terminated quickly enough after pore fabrication and the location of the nanopore on the membrane can be random. For some applications, such as those involving nano-electrodes that measure transverse tunneling current, nanostructures on the membrane surface that control capture and/or passage of biomolecules, or for experiments involving optical detection, precise localization of the nanopore may be important. Thus, the CBD technique may be difficult to implement.
This section provides background information related to the present disclosure which is not necessarily prior art.